Disc drives of the type known as "Winchester" disc drives, or hard disc drives, are well known in the industry. Such disc drives magnetically record digital data on a plurality of circular, concentric data tracks on the surfaces of one or more rigid discs. The discs are typically mounted for rotation on the hub of a brushless DC spindle motor. In disc drives of the current generation, the spindle motor rotates the discs at speeds of up to 10,000 RPM.
Data are recorded to and retrieved from the discs by an array of vertically aligned read/write head assemblies, or heads, which are controllably moved from track to track by an actuator assembly. The read/write heads typically consist of an electromagnetic transducer carried on an air bearing slider. This slider acts in a cooperative hydrodynamic relationship with a thin layer of air dragged along by the spinning discs to fly the head in a closely spaced relationship to the disc surface. In order to maintain the proper flying relationship between the heads and the discs, the heads are attached to and supported by head suspensions or flexures.
The actuator assembly used to move the heads from track to track has assumed many forms historically, with most disc drives of the current generation incorporating an actuator of the type referred to as a rotary voice coil actuator. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the disc drive housing base member closely adjacent the outer diameter of the discs. The pivot shaft is mounted such that its central axis is normal to the plane of rotation of the discs. An actuator bearing housing is mounted to the pivot shaft by an arrangement of precision ball bearing assemblies, and supports a flat coil which is suspended in the magnetic field of an array of permanent magnets, which are fixedly mounted to the disc drive housing base member. On the side of the actuator bearing housing opposite to the coil, the actuator bearing housing also typically includes a plurality of vertically aligned, radially extending actuator head mounting arms, to which the head suspensions mentioned above are mounted. When controlled DC current is applied to the coil, a magnetic field is formed surrounding the coil which interacts with the magnetic field of the permanent magnets to rotate the actuator bearing housing, with the attached head suspensions and heads, in accordance with the well-known Lorentz relationship. As the actuator bearing housing rotates, the heads are moved radially across the data tracks along an arcuate path.
Disc drives of the current generation are included in desk-top computer systems for office and home environments, as well as in laptop computers which, because of their portability, can be used wherever they can be transported. Because of this wide range of operating environments, the computer systems, as well as the disc drives incorporated in them, must be capable of reliable operation over a wide range of ambient temperatures.
Furthermore, laptop computers in particular can be expected to be subjected to large amounts of mechanical shock as they are moved about. It is common in the industry, therefore, that disc drives be specified to operate over ambient temperature ranges of from, for instance, -5.degree. C. to 60.degree. C., and further be specified to be capable of withstanding operating mechanical shocks of 100 G or greater during disc drive operation. Moreover, future disc drive products are being developed which must be capable of withstanding non-operating shocks of up to 1000 G without becoming permanently inoperable.
One area of concern regarding mechanical shock tolerance is the structure used to mount and support the read/write heads within the disc drive. The head suspension, or flexure, which mounts and supports the heads consists of several portions which each have a specific function:
a mounting portion, usually stiffened by a relatively thick mounting plate, which is used to mount the head/flexure assembly to the moving actuator of the disc drive;
a load spring portion, adjacent the mounting portion, which serves to provide a downward (toward the disc surface) load force which counter-balances the hydrodynamic lifting force of the slider body carrying the read/write transducers to establish the desired flying height of the head;
a stiffened beam portion, extending from the load spring portion, which serves to transfer the load force of the load spring portion, and;
a gimbal portion, located at the distal end of the stiffened beam portion, which actually mounts the head, and is compliant in the head's roll and pitch axes, to allow the head to conform to minor variations in the surface of the discs, and stiff in the head's yaw and in-plane axes, to provide accurate positioning of the head's transducer relative to data recorded on the disc.
The gimbal portion also typically includes a load point dimple, or etched load point button, which provides a point-contact location for the application of the load force generated by the load spring portion to the head. Some prior art head suspension assemblies do not include such a load point dimple or load point button.
Design compromises in prior art head suspension assemblies contribute to an undesirable phenomenon typically referred to in the industry as "head slap". Head slap occurs when mechanical shocks are applied to the disc drive in an axis which causes the load force of the load spring portion of the head suspension to be overcome, allowing the head to rise away from its intended operational position with the disc. The head typically is held to the disc surface by a liquid miniscus. However, the stiffened beam portion of the head suspension is typically about ten times as massive as the gimbal and head combined, so that when the stiffened beam portion moves away from the disc in response to the application of mechanical shock, the head tends to remain in contact with the disc surface, and the gimbal portion of the head suspension deforms as the stiffened beam portion moves away from the disc. If the deflection of the stiffened beam portion is small enough, the head may remain in the proper relationship to the disc. If, however, the deflection of the stiffened beam is great enough, the force developed in the deforming gimbal portion becomes great enough to overcome the liquid miniscus between the head and the disc and the head is forced away from the disc toward the deflected stiffened beam portion.
At the termination of the shock event, the load force of the load spring portion of the head suspension causes the head to accelerate back toward the disc, and to cause direct, uncontrolled contact between the head and the disc. Such uncontrolled contact can readily result in damage to the disc surface or the head, either of which can be fatal to the proper operation of the disc drive.
The present invention is directed to prevention of such head slap events, thus increasing the disc drive's tolerance to applied mechanical shocks, and increasing the overall reliability of the disc drive.